Joint Seminar by SKL, ECE Dept and SID - Flexoelectric in Liquid Crystals and Its Applications
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Nematic liquid crystals of specially shaped molecules, such as “banana” and “pear” shaped, in special confinements or configurations exhibit spontaneous electric polarization, a phenomenon known as flexoelectric effect. They can be reoriented by externally applied electric fields through two interactions. One is the regular dielectric interaction, which is not sensitive to the polarity of the applied voltage. The other one is felxoelectric interaction, which is sensitive to the polarity of the applied voltage. The dielectric and flexoelectric interactions have different dependences on the frequency of the applied voltage. Flexoelectric interaction is dominant in low frequency region (~10 Hz) and can align the liquid crystal in one direction, while dielectric interaction is dominant in high frequency region (~1000 Hz) and can align the liquid crystal in another direction. Therefore the liquid crystal can be switched to different states by varying the frequency of the applied voltage. The flexoelectric and dielectric effects can be made use to develop many devices, which are impossible under only dielectric interaction. In my talk, I will discuss the mechanism of flexoelectric effect. I will also discuss its applications, such as reconfigurable optical grating, light waveguide liquid crystal display, dual mode smart switchable window and bistable polymer stabilized cholesteric texture smart window.
Deng-Ke Yang is a professor in the School of Emergent Soft Matter at South China University of Technology. He received his B.S. in physics from Tsinghua University in China in 1984 and his Ph.D. in physics from University of Hawaii in 1989. He worked as postdoctoral fellow, assistant professor, associate professor and full professor in Kent State University from 1989 to 2025. His main research interest is in liquid-crystal physics and devices. He has coauthored 2 books and 8 book chapters. He also has published more than 200 papers. He received the Society for Information Display (SID) Special Recognition Award in 2005 for his pioneering work on polymer-stabilized cholesteric devices and reflective displays. He was elected as a fellow of the SID in 2007 for his significant scientific and technological contributions to bistable, reflective cholesteric displays and to polymer-stabilized cholesteric devices, and for his outstanding contributions to education. He received SID Slottow-Owaki Prize in 2017 for his outstanding contributions to the education and training in the field of liquid-crystal displays. He also received Kent State University annual Outstanding Research and Scholarship Award in 2017. He has been named one of the world’s top 2% of scientists by Stanford University.